#include<iostream>
using namespace std;
int main(){
    int n,a,b,l=1,m=1;
    cin>>n;
    cin>>a;
    for(int i=2;i<=n;i++){
        cin>>b;
        if(b==a+1)    l++;
        else if(l>m) {
            m=l; l=1;
        }
        a=b;
    }
    cout<<m;
    return 0;
}